1. Field of the Invention
The present invention relates to an apparatus and method for providing seamless service between a cellular network and a Wireless Local Area Network (WLAN) for a mobile user. More particularly, the present invention relates to an apparatus and method for providing cellular network services using the WLAN seamlessly.
2. Description of the Related Art
Mobile terminals provide wireless communication between users. As technology has advanced, mobile terminals now provide many additional features beyond simple telephone conversation. For example, mobile terminals are now able to provide additional functions such as an alarm, a Short Messaging Service (SMS), a Multimedia Message Service (MMS), E-mail, games, remote control of short range communication, an image capturing function using a mounted digital camera, a multimedia function for providing audio and video content, a scheduling function, and other similar functions provided on portable electronic devices. With the plurality of features and functions now provided, mobile terminal users consume increasing amounts of wireless communication services provided by a cellular communication system.
Accordingly, a cellular radio spectrum, which is used for providing the wireless communication services noted above, is limited, and thus the cellular radio spectrum provides a limited amount of cellular resources for the increasing amounts of wireless traffic. To address the limited cellular resources, recent research and development has been directed towards providing greater amounts of wireless resources for mobile end users and User Equipments (UEs) using cellular resources. For example, research has been conducted on providing Institute for Electrical and Electronics Engineers (IEEE) 802.11 or Wireless-Fidelity (Wi-Fi) networks operating in conjunction with, or on top of, cellular networks in order to decrease an amount of cellular resources used by UEs. Accordingly, a brief description of cellular networks and the operation of cellular networks is provided below.
FIG. 1A illustrates a control plane of a cellular network according to the related art. FIG. 1B illustrates a user plane of a cellular network according to the related art.
Referring to FIGS. 1A and 1B, in a wireless communication system using the cellular radio spectrum, i.e., a cellular radio network or cellular network, a UE is connected to a Radio Access Network (RAN) through a cellular radio link, and the RAN is connected to a core network, which may include, a Base Station (BS), a Mobile Switching Center (MSC), General Packet Radio Service (GPRS) Support Node (GSN), or other similar items and elements included in a core network. The RAN uses a radio resource allocation procedure in order to establish a radio link. The cellular network system, which is operated on the RAN, is composed of two planes, a control plane 101 for interconnecting network elements for signaling, as shown in FIG. 1A, and a user plane 201 for interconnecting network elements for data, such as voice data, graphics data, and other similar user data, as shown in FIG. 1B.
In further detail, the RAN, which may also be referred to as a BS Subsystem (BSS), may be composed of at least one Node-B as a radio transceiver that provides a radio cell unit, and a Radio Network Controller (RNC), which controls the at least one Node-B. Accordingly, the RAN provides the UE access to the RAN by controlling connections between the UE and the RAN. For example, a Non-Access Stratum (NAS) 102 is a top layer of a protocol interface between the UE and the core network via an MSC and/or GSN, and provides call and data session setup as well as management of the UE in order to manage the entry, exit and handover of the UE.
Additionally, the NAS 102 may provide a Circuit Switched (CS) call service and a Packet Switched (PS) data service between the UE and the core network via the RAN. Radio Resource Control (RRC) 103 is a layer disposed below the NAS 102, and the RRC 103 provides radio resource control between a UE and the RAN. Particularly, the RRC 103 provides a negotiation of radio resources between the UE and the RAN in order to establish a radio connection, wherein during the negotiation, both the UE and the RAN exchange radio parameters and states through the RRC 103 protocol interface. Additionally, the RRC 103 provides connection and mobility management by establishing and tearing down connections while the UE roams among a cell, monitors and controls a radio condition by determining a radio link quality of a cell in which the UE is roaming in or disposed, and manages connection states with the RAN.
Radio Link Control (RLC) 104 provides communication between the RRC 103, or other similar upper layers such as Broadcast/Multicast Control (BMC) and Packet Data Convergence Protocol (PDCP), and logical channels of the wireless communication system. More particularly, the RLC 104 provides frame transmission between the UE and the RAN. Accordingly, the RLC 104 performs segmentation and reassembly of data transmitted between the UE and the RAN, performs error detection and recovery, and may perform ciphering and deciphering of control messages sent between the UE and the RAN. The RLC 104 may operate in three modes, an Acknowledged Mode (AM), a Transparent Mode (TM), and an Unacknowledged Mode (UM) according to a desired control of signaling and traffic data between the UE and RAN.
Furthermore, Media Access Control (MAC) 105 maps logical channels to transport channels of the Physical layer. The MAC 105 performs multiplexing of logical channel data and is responsible for managing a Hybrid Automatic Repeat Request (HARQ) function. The MAC 105 also performs priority handling of the data flows, such that, when there are multiple transmission sessions, the MAC 105 handles dynamic scheduling of transmissions for each session so that higher priority data transmissions receive a corresponding priority. The MAC 105 may also perform traffic volume monitoring and may provide ciphering and deciphering of voice data.
Referring to FIG. 1B, the user plane includes the RLC 104 and the MAC 105, among other layers and features, which will not be described herein for the purpose of brevity. Additionally, the RLC 104 and the MAC 105 of the user plane of FIG. 1B are similar to the RLC 104 and the MAC 105 as described with reference to the control plane illustrated in FIG. 1A. Additionally, a UE may use CS services for transmission of voice frames such that a frame is sent every 20 ms, i.e., at a rate of 50 frames per second, via the RLC 104 and the MAC 105. The voice frame may be sent from the UE to the core network via the RAN by using the RLC 104 and the MAC 105, which dynamically determine transport options for each transmission according to a configuration set determined during the radio resource allocation stage. The UE may also use PS services for transmission of data packets in a periodic mode, a burst mode, or another suitable transmission mode, that is selected by the RLC 104 and the MAC 105 according to a configuration set determined during the radio resource allocation stage. The data packets are transmitted from the UE to the RAN using a Packet Data Convergence Protocol (PDCP), and the RAN converts the PDCP into General Packet Radio Service (GPRS) Tunneling Protocol (GTP) in order to relay the data packets to the core network.
FIG. 2 illustrates a signal flow for a voice call originated by a UE according to the related art.
Referring to FIG. 2, a wireless communication system includes a MSC/GSN 201, a RNC 202, a Node-B 203 and a UE 204. In order to perform a voice call originated from the UE 204, at step 205, the UE 204 transmits an RRC connection request message to the RNC 202 via the Node-B 203 in order to request a radio resource allocation. Next, at step 206, the RNC 202 allocates traffic channel radio resources for the UE 204 and sends a command to the Node-B 203 to setup a physical radio resource for the UE 204, after which, the Node-B 203 and the RNC 202 may perform a low layer synchronization process for the new traffic channel. Next, in step 207, the RNC 202 transmits an RRC Connection Setup message to the UE 204 when the RNC 202 and the Node-B 203 have prepared the radio resource in order to inform the UE 204 that the radio resource assignment has been completed.
Upon receiving the RRC connection setup message, the UE 204 selects or tunes to the radio resource prepared by the RNC 202 and the Node-B 203 in order to establish a radio link with the Node-B 203. Next, in step 208, upon detecting that the UE 204 has established a radio link, the Node-B 203 transmits a Node-B Application Part (NBAP) Radio Link Restore Indication message to the RNC 202. Next, in step 209, the UE 204 transmits a RRC connection setup complete message to the RNC 202, and then, in step 210 the RNC 202 sends an RRC Measurement Control message to the UE 204 initiate reporting of the link status between UE 204 and the RAN. Next, in step 211, the UE 204 transmits an Initial Direct Transfer-Connection Management service request message to start a NAS session procedure for initiating a call setup, and, upon receiving the service request message from the UE 204, the MSC/GSN 201 performs an authentication and ciphering process between UE 204 and the MSC/GSN 201.
Next, in step 212, the UE sends Direct Transfer-Call Control (DT-CC) setup message to the MSC/GSN 201, which then allocates a voice circuit from a digital trunk between the RNC 202 and the MSC/GSN 201. Next, in step 213, the MSC/GSN 201 transmits a DT-Radio Bearer Assignment message to inform the RNC 202 about the allocated voice circuit, and the call is then switched from a signaling mode to a voice mode. In step 214, the connection between the Node-B 203 and the RNC 202 is switched from a signaling mode to a voice call mode. Next, in step 215, the RNC 202 transmits a RRC-Radio Bearer Setup message to the Node-B 203 in order to request the Node-B 203 to perform the mode change for the traffic channel through a NBAP-Radio Link Reconfigure Preparation (NBAP-RLRP) message and also notifies the UE about the mode change through the NBAP-RLRP message. Next, in step 216, when a destination for the call, i.e., a peer, accepts the call, then the MSC/GSN 201 sends a DT-CC Connect message to the UE 204. Accordingly, the UE 204, may originate and connect a voice call.
Furthermore, the mobile communication system may include a femtocell for providing additional and/or extended wireless coverage for UEs. A femtocell has an approximate coverage area of 100 feet, and uses similar technology as described with reference to FIGS. 1A, 1B, and 2. In other words, the femtocell may use a cellular protocol interface via a cellular radio modem, thus using the control plane of FIG. 1A and the user plane of FIG. 1B, and thus may interoperate with the elements of the wireless communication system of FIG. 2. However, the femtocell has several disadvantages, wherein, because the femtocell operates on a cellular radio frequency band, it may cause radio interference with neighboring macro BSs. Additionally, each femtocell is determined to be one radio cell, thus when deployed widely in large numbers, each having an approximate coverage area of 100 feet, use of femtocells increases an amount of configuration and management of a wireless communication system. Accordingly, although use of femtocells may increase for certain applications, such as providing coverage in cellular network shadows or high density locations, large scale deployment of femtocells increases cost as well as configuration and management complexity of wireless communication systems.
Additionally, in order to provide increased amounts of bandwidth to UEs, cellular network providers have implemented Unlicensed Mobile Access (UMA), which may also be referred to as Generic Access Network (GAN), in order to extend voice, data, and Internet Protocol (IP) services of the cellular network providers. UMA is a different protocol interface than that of the cellular network or wireless communication system described with reference to FIGS. 1A, 1B, and 2. However, UMA provides similar functionality as the above described wireless communication system and may operate using an unlicensed network, such as a Wireless Local Area Network (WLAN) that does not use the cellular radio frequency band. Accordingly, UMA does not require installation of additional radio access system hardware in a cellular wireless communication system, while providing seamless services between a cellular network and a WLAN network.
However, because UMA is a protocol interface operating in conjunction with a cellular network, UMA may not provide all radio communication features that a cellular network provides. Accordingly, UMA may not operate reliably in complicated and unreliable radio network environments, such as a cellular network, and thus, may not provide stable and reliable voice and data services and may not provide the robustness or number of functions available via a cellular network. Additionally, because UMA is a different protocol interface than that of a cellular network, deployment of UMA in a cellular network includes providing a gateway for translating the UMA protocol into the cellular network protocol, thus, increasing a cost and complexity of cellular network implementing UMA. Furthermore, because of the necessary translation between the UMA protocol and the cellular protocol, changes to a cellular protocol or deployment of a new cellular protocol may require a corresponding change to the UMA protocol and a corresponding UMA gateway in order to provide a translation between the UMA protocol and the new cellular protocol interface. Due to the foregoing complexities and problems with UMA deployment, many operators are either discontinuing deployment of, or limiting the usage of, UMA. Accordingly, there is a need for an apparatus and method for providing an improved WLAN access or UMA seamlessly through a cellular protocol interface.